I go through periods of waking up at 3AM or thereabouts and not being able to go back to sleep. I often start thinking about something I'm working on and wind up in my office where I wake up my computer and ... wham! My retinas are fried. A screen brightness level that's appropriate for day time is simply painful at 3AM.

makes the color of your computer's display adapt to the time of day, warm at night and like sunlight during the day.

The authors of f.lux point out that:

It's even possible that you're staying up too late because of your computer. You could use f.lux because it makes you sleep better, or you could just use it just because it makes your computer look better.

I tried f.lux on my iMac and while it does make the screen far less blinding it only does so on a schedule that's linked to your local time. This means that at around my local sunset f.lux will change my screen from a color temperature of daylight (6500K ... very white) to, for example, Halogen (3400K ... a softer golden hue) or Tungsten (2700K very yellow) or even candle (2300K ... this setting should really flicker).

The problem is that I often work until late into the evening so unless I choose a timezone that's about 4 or 5 hours behind me I'll wind up with a display that's soft on the eyes but with untrue colors. This will be a problem if I'm editing photos or doing anything else graphical but f.lux lets you do is delay the color shift for an hour on demand (it would be nice for this delay to be set to a higher value or, even better, a specific time).

f.lux is available for OS X, Windows, and Linux and even for iOS. Now, iOS would be great because sometimes at 3AM what I want to do is read on my iPad but, alas, f.lux only works on jailbroken iDevices because, to work its magic, it has to run in the background and Apple is loathe to allow such behavior. f.lux is a great idea and Apple needs to reconsider.